It's a puzzler. There is an overwhelming amount of circumstantial evidence, of the kind that has formed the basis for many a murder or manslaughter conviction.
One of the suspects is a top lawyer at powerful firm. Either he has connections that have worked to protect him behind the scenes, or the DC Police Dept is thoroughly incompetent, or both.
But it appears these three gentlemen are getting away with, at worst, murder, at best, some form of manslaughter, whether voluntary or involuntary, or perhaps negligent homicide if there was no criminal intent (e.g., sex play that went awry). Re that last, however, the substantial evidence of tampering with evidence/obstruction of justice certainly adds to the gravity of the crime, even if the actual death was an accident.
It appears the police have completely botched the investigation. It's a real tragedy.
Nice to see the WaPo has picked up the story again, although they seem to be handling it with kid gloves. A DC blog has been covering the investigation (such as it is) for the past two years. A good resource:
http://whomurderedrobertwone.com/
Same exact facts, involving black gays in a poor section of DC, you can bet your ass two of the three suspects would be behind bars awaiting trial or already convicted, with the third perhaps getting a light sentence for testifying against the other two.